In systems for counting blood cells or other particles suspended in a liquid sample, a pair of electrodes are provided within a fluid path having an aperture disposed therebetween through which the particle-containing liquid flows. The impedance of the fluid path as sensed by the electrodes is materially altered by the presence of a particle within the aperture giving rise to electrical pulses which are electrically counted and which correspond to the number of particles passing through the aperture. Means are usually employed for metering a known volume of particle-containing liquid such that a particle count is provided for a predetermined liquid volume. In the hematological analysis of blood a variety of parameters in addition to cell counts are useful and have been provided either by respective analytical instruments or by relatively complex multiple parameter systems.